A video from a researcher could spell curtains for one of the key patents in Apple’s ongoing litigation against Samsung.

The 1991 video, entitled “Touchscreen Toggle Design,” features University of Maryland researcher Catherine Plaisant showing off a number of ways to model a touchscreen toggle that users can control. One of the toggles (shown at around 2:55) is an on-off slider that users can control by swiping their finger back and forth, in a manner that’s similar to Apple’s slide-to-unlock control for the iPhone.

That’s a problem for Apple, which argues that Samsung’s phones violate its patent on the slide-to-unlock gesture. The video, which pre-dates Apple’s patent by more than a decade, could serve as prior art that shows the patent is invalid. According to Florian Mueller over at FOSS Patents, Apple has argued in the past that Plaisant’s video doesn’t count because the company’s patent governs sliding to unlock, and an on/off switch is different than that.

Saying that a sliding on/off switch is different than a slide to unlock switch just because one of them unlocks and the other doesn’t is a fairly weak argument, but it seems like that’s all Apple has. Mueller pointed out that Apple’s patent has been deemed invalid in Europe because of similar functionality present in the Swedish Neonode N1M. Right now, there’s some dispute over whether or not a Swedish phone could be considered prior art when it comes to Apple’s patent in the U.S.

Still, even if the slide to unlock patent is invalid, Apple still has a number of other patents that it claims Samsung infringes. Another Apple patent at issue in the current lawsuit governs “rubber banding,” which allows users to slightly scroll past the top of a document or view before it bounces back into place.

[This post has been updated to correct Plaisant’s employer.]

Blair Hanley Frank is GeekWire's Bay Area Correspondent. He has also worked for Macworld, PCWorld and TechHive. Follow him on Twitter @belril and email him at blair@geekwire.com.